Indigo carmine, chemically known as 3,3′-dioxo-2,2′-bis-indolyden-5,5′-disulfonic acid disodium salt, commonly used as a pH indicator, often in a 0.2% aqueous solution. It is blue at pH 11.4 and yellow at 13.0. Indigo carmine is also a redox indicator, turning yellow upon reduction. Another use is as a dissolved ozone indicator through the conversion to isatin-5-sulfonic acid. This reaction has been shown not to be specific to ozone, however: it also detects superoxide, an important distinction in cell physiology. It is also used as a dye in the manufacturing of capsules.
In obstetric surgery, indigo carmine solutions are sometimes employed to detect amniotic fluid leaks. In urologic surgery, intravenous injection of indigo carmine is often used to highlight portions of the urinary tract. The dye is filtered rapidly by the kidneys from the blood, and colors the urine blue. This enables structures of the urinary tract to be seen in the surgical field, and demonstrate if there is a leak. However, the dye can cause a potentially dangerous increase in blood pressure in some cases.
Indigo Carmine is excreted largely by the kidneys, retaining its blue color during passage through the body. Elimination of the dye begins soon after injection, appearing in the urine within 10 minutes in average cases. The biological half-life is 4 to 5 minutes following intravenous injection. Larger quantities are necessary when intramuscular injection is employed. Appearance time and elimination are delayed following intramuscular injection.
As described FDA indications of indigo carmine: Originally employed as a kidney function test, the chief application of Indigo Carmine at present is localizing ureteral orifices during cystoscopy and ureteral catheterization
Dye and pigments 6, page-135-154(1985) describes process for making trisulpho, disulpho, mono sulpho Indigo. In accordance with the journal, Indigo can prepared by reacting sulphuric acid as well as 30% fuming sulphuric acid, here they disclosed the disulphonic indigo will preparation temperature at 100° C. but not describe process or any analytical data forming disulphonic salt of indigo. In this journal process Indigo carmine compound is not isolating or not easy filtration, also Indigo carmine not getting having purity as per the ICH guideline.
Bull. Chem. Soc. Jap. Vol. 84, no. 1, page-82-89(2011), intermediate of Indigo, process describe using Molybledenumhexacarbonyl as catalyst, in presence of acid as acetic acid or phenyl acetic acid or additive, oxidizing agent cumene hydroperoxide (CHP) in cumene (82%) solution using alcohol, in this publication large amount of catalyst (0.05 mol) and large amount of solvent using.
U.S. Pat. No. 1,427,863 describe process for preparing indigo (isatina-anilid) using thioaminde, sulphuric acid, ammoniumsulphite, water.
U.S. Pat. No. 1,588,960 describe process for making indigo using aniline oxidizing in acid solution to produce chromophore blue treated with organic acid to give indigo.
GB181673 describe process for preparing indigo using mineral oil, sodamide, sodium salt of phenyl glycine/hydroxyethyl aniline and mixture of caustic soda and caustic potash.